Can anyone help me in installing mysql 5.7.
I tried following this answer, but when I run

sudo apt-cache policy mysql-server

It gives me:

8.0.20-0ubuntu0.20.04.1 500

    500 http://pk.archive.ubuntu.com/ubuntu focal-updates/main amd64 Packages

    500 http://pk.archive.ubuntu.com/ubuntu focal-updates/main i386 Packages

    500 http://security.ubuntu.com/ubuntu focal-security/main amd64 Packages

    500 http://security.ubuntu.com/ubuntu focal-security/main i386 Packages

8.0.19-0ubuntu5 500

    500 http://pk.archive.ubuntu.com/ubuntu focal/main amd64 Packages

    500 http://pk.archive.ubuntu.com/ubuntu focal/main i386 Packages

5.7.31-1ubuntu18.04 500

    500 http://repo.mysql.com/apt/ubuntu bionic/mysql-5.7 amd64 Packages

5.7.30-0ubuntu0.18.04.1 500

    500 http://security.ubuntu.com/ubuntu bionic-security/main amd64 Packages

    500 http://security.ubuntu.com/ubuntu bionic-security/main i386 Packages

Which are different from the linked answer.

When I tried to

sudo apt install -f mysql-client=5.7.30-1ubuntu18.04

It gives me error

Version '5.7.30-1ubuntu18.04' for 'mysql-client' was not found.

When I run sudo apt install -f mysql-client-5.7 command it installed mysql version.
I also does not finds mysql-community-server=5.7.30-1ubuntu18.04.

I tried to run sudo apt install -f mysql-community-server It gives me following error:

mysql-community-server : Depends: mysql-client (= 5.7.31-1ubuntu18.04) but 8.0.20-0ubuntu0.20.04.1 is to be installed